Marine biofouling, membrane fouling, insect adhesion on aircraft surfaces, microbial contamination of sterile environments, and surface particle contamination all present unique challenges. An array of mitigations strategies has been pursued to address these problems.
Passive strategies for minimizing fouling or contamination of surfaces are beneficial especially in environments where active mitigation of the fouling or contamination is impractical or impossible. For instance, lunar dust compromised seals, clogged filters, abraded visors and space suit surfaces, and was a significant health concern during the Apollo missions. Accordingly, passive mitigation utilizing materials with an intrinsic resistance to surface contamination would be advantageous for such applications. One passive mitigation strategy is modification of a material's surface energy either chemically or topographically or both.
Any surface material needs to meet the requirements of its application. High performance polymeric materials have been developed to address various requirements for mechanical, thermal, and optical properties. Modification of the chemical constituency of these polymeric materials can alter their properties. Thus, modification of high performance polymeric materials is often hampered due to degradation of the desired characteristic properties. Modifying a polymeric material to influence surface characteristics is problematic as addition of sufficient modifier to the bulk chemical composition to achieve the desired surface modification could also result in the diminution of other important performance properties of the polymeric material. If the modifier is well dispersed within the polymer matrix, a majority of the modifier will be located in the interior of the polymeric structure where it will not contribute to the structure's surface properties. This is especially problematic if the modifier is expensive, provides no other performance enhancement or diminishes bulk properties of the polymeric material.
Polymeric materials with low adhesion surface properties have been demonstrated to be effective in a wide variety of applications. Low surface energy polymeric materials, i.e., those exhibiting a high water contact angle, have been used to reduce marine biofouling, water and ice adhesion, and biofilm formation; to improve oxidation, corrosion and stain resistance; to minimize dust adhesion; and to modify the performance of microfluidic systems and biomedical devices. The ability to selectively modify the surface energy of high performance polymeric materials without sacrificing their superior mechanical, thermal and optical properties is of significant utility.
A number of approaches have been suggested to yield polymeric materials with low surface energy. One of the most well known polymeric materials having low surface energy are fluorinated, aliphatic polymers such as those available under the trade name TEFLON® fluoropolymers. The presence of both aliphatic carbon species and fluorine atoms contributes to the low surface energy of this class of materials. These polymeric materials have an approximate homogeneous composition, do not use a controlled modification, and thus cannot be tailored for the introduction of further surface features. Moreover, they do not adhere well to substrates and are difficult to process. Generally the polymer is provided as a powder to be coated and sintered onto the substrate. Another approach is to vapor deposit highly fluorinated carbonaceous materials to various substrates.
Another approach to provide low surface energy polymeric materials is to incorporate surface modifying agents into the materials. These surface modifying agents are thermodynamically driven to migrate to the surface of the polymeric material preferentially due to more favorable interactions at the air interface compared to the polymeric matrix.
Omnova Solutions Inc. offers a family of hydroxyl terminated oxetane-derived oligomers under the trade name POLYFOX® fluorochemicals and have found commercial application in polymeric systems. Fluorine-containing oxetane derivatives have been used extensively as surface modification agents for modification of urethanes. See, for instance, Malik, et al., United States patent application publication No. US 2004/0087759. Medsker, in U.S. Pat. No. 7,022,801 and Thomas, et al., in United States patent application publication No. 2003/0092862, disclose the use of fluoro-containing oxetane polymers to impart wetting, flow or leveling properties to a variety of coatings while producing little foam.
Wynne, U.S. Pat. No. 7,396,590 and Wynne, et al., in U.S. Pat. No. 7,771,793 disclose making polymeric articles or coatings that have a surface phase having an activity of interest. They disclose preparing a surface active telechelic that includes both a surface active segmer which favors migration to the surface of a bulk polymer and one or more functional segmers which provide an activity of interest (e.g., biocide, bioactive, UV protective, hydrophobic, hydrophylic, etc.). The telechelics disclosed include those made using fluorine-containing oxetanes.
Weinert, et al, in U.S. Pat. No. 6,972,317 disclose monofunctional polyfluorooxetane oligomers and polymers that can be reacted with cyclic ethers or functionalized with a functional end group such as an acrylate, a methacrylate, an allylic, an amine, etc., for use in radiation curable or thermal curable coating compositions. They believe that the fluorinated side groups of the fluorooxetanes are disproportionately present at the interfaces between the coating and substrate and between the coating and the atmosphere.
Polyimides are known for their thermal stability, fire resistance, good chemical resistance and excellent mechanical properties. Polyimides have good mechanical elongation and tensile strength and good adherence properties to many substrates. Some polyimides exhibit high optical clarity. Polyimides have found application as coatings, insulating films in the electronic industry, fibers and articles of manufacture including for demanding applications such as bushings, bearings in jet engines, or other constructive parts.
Accordingly, a need exists for a low surface energy polymeric material that has the mechanical, thermal, chemical and optical properties associated with polyimides.